Aquation

About: Aquation is a research topic. Over the lifetime, 1443 publications have been published within this topic receiving 17507 citations.

Novel ruthenium(III) dimers Na2[{trans-RuCl4(Me2SO-S)}2(µ-L)] and [{mer,cis-RuCl3(Me2SO-S)(Me2SO-O)}2(µ-L)] (L = bridging heterocyclic N-donor ligand) closely related to the antimetastatic complex Na[trans-RuCl4(Me2SO-S)(Him)]†

Abstract: The symmetrical dianionic and neutral ruthenium(III) dimers Na2[{trans-RuCl4(Me2SO-S)}2(µ-L)] 1 and [{mer,cis-RuCl3(Me2SO-S)(Me2SO-O)}2(µ-L)] 3 (L = pyrazine 1a, 3a; pyrimidine 1b; 4,4′-bipyridine 1c; 1,2-bis(4-pyridyl)ethane 1d; or 1,3-bis(4-pyridyl)propane 1e), which represent unprecedented examples in the general Creutz–Taube family of ruthenium dimers, were developed with the specific aim of assessing their antineoplastic properties. Each ruthenium center in 1 and 3 has a co-ordination environment similar to that of known anionic and neutral monomeric ruthenium(III) complexes endowed with a specific antimetastatic activity against animal model tumors. Beside the synthesis and spectroscopic characterization of the new dimers, and the structural characterization of 1a, 1b, 1c, and 3a, a thorough investigation of their chemical behavior in aqueous solution was made. At 25 °C and pH 7.4 the dianionic species 1a–1e maintain their dimeric structure and undergo rather slow stepwise chloride hydrolysis to yield the relatively inert diaqua species [{mer,cis-RuCl3(Me2SO-S)(H2O)}2(µ-L)]. At physiological pH dimers 1a–1e are also easily and quantitatively reduced by equivalent amounts of ascorbic acid to the corresponding RuII/II dimers which, in turn, undergo stepwise aquation with rates roughly comparable to those of the RuIII/III species of equal net charge. Since the reduction processes might occur also in vivo, the chemical behavior of the RuII/II dimers is relevant to understanding the biological mechanism of action of these compounds and was thus investigated in detail. The neutral dimer 3, which is scarcely soluble in aqueous solution, gives soluble dimeric species upon reduction with ascorbic acid. We found that reduction is accompanied by O to S linkage isomerization and by partial dissociation of the equatorial dmso. Overall, the dimeric structures of the new compounds are quite robust, both in the RuIII/III and in the RuII/II form, and they undergo aquation reactions similar to those of the monomeric analogs. However, while the monomeric species after aquation are either mono- or bi-functional binders, the new dimers might behave as bi- or even tetra-functional binders. Thus, it is likely that their interaction with biological targets might lead to adducts which are not accessible to the mononuclear species.

Photoaquation Mechanism of Hexacyanoferrate(II) ions: Ultrafast 2D UV and Transient Visible and IR Spectroscopies

Abstract: Ferrous iron(II) hexacyanide in aqueous solutions is known to undergo photoionization and photoaquation reactions depending on the excitation wavelength. To investigate this wavelength dependence, we implemented ultrafast two-dimensional UV transient absorption spectroscopy, covering a range from 280 to 370 nm in both excitation and probing, along with UV pump/visible probe or time-resolved infrared (TRIR) transient absorption spectroscopy and density functional theory (DFT) calculations. As far as photoaquation is concerned, we find that excitation of the molecule leads to ultrafast intramolecular relaxation to the lowest triplet state of the [Fe(CN)6]4– complex, followed by its dissociation into CN– and [Fe(CN)5]3– fragments and partial geminate recombination, all within <0.5 ps. The subsequent time evolution is associated with the [Fe(CN)5]3– fragment going from a triplet square pyramidal geometry, to the lowest triplet trigonal bipyramidal state in 3–4 ps. This is the precursor to aquation, which occu...

Photolytic and radiolytic study of platinum(III) complex ions containing aquo and chloro ligands

Abstract: The formations and characterizations of short-lived, monomeric platinum(III) complex ions containing aquo and chloro ligands have been studied by using pulse radiolysis and laser photolysis techniques coupled with uv-visible absorption and conductivity detection methods. Five different chemical routes have been used to generate in aqueous media the same or similar platinum(III) species: reaction of tetrachloroplatinum(II), (PtCl{sub 4}){sup 2{minus}}, with the hydroxyl radical, interactions of hexachloroplatinum(IV), (PtCl{sub 6}){sup 2{minus}}, with the hydrated electron, hydrogen atom, and tert-butyl alcohol radical, and the 265-nm photolysis of (PtCl{sub 6}){sup 2{minus}} with the latter giving rise to both oxidation-reduction and ligand-substitution processes. The platinum(III) Intermediates can be classified into two categories. The nascent or shorter lived species exhibit intense charge-transfer bands with peak maxima near 450 nm or at wavelengths below 300 nm, and they are proposed to be of a distorted-octahedral type with compositions of the form (Pt{sup III}-(Cl){sub 6-m}(X){sub m}) (m = 0-2; X = OH, H{sub 2}O). The longer lived Pt(III) complexes are characterized by a single charge-transfer band having a peak between 410 and 420 nm and by compositions of the type (PtP{sup III}(Cl){sub 4-n}(X){sub n}) (n = 1-3; X = OH, H{sub 2}O) having limiting square-planar structures. The mechanisms formore » the formations of the platinum(III) complex ions and for their interrelationships are discussed, and evidence is presented to indicate that these species act as catalytic agents in the thermal aquation of (PtCl{sub 6}){sup 2{minus}}. 43 refs., 7 figs., 3 tabs.« less

Mechanistic information from a volume profile treatment for the complexation of aquocobalamin (vitamin B12a) by pyridine

Abstract: The complexation kinetics of aquocobalamin (vitamin B 12a ) by pyridine was studied as a function of pyridine concentration, temperature, and pressure. This kinetic data equally well fit D and I d mechanisms. The pressure dependence of the rate and equilibrium constants enables the construction of an overall reaction volume profile, from which it is concluded that both the forward complex formation and reverse aquation reactions proceed according to a limiting D mechanism